The program objective is to facilitate the management of the NIH Animal Genetic Resource (NIHAGR) through development and utilization of embryolgamete collection and handling techniques for cryobanking genetic material and improving reproductive potential. The NIHAGR maintains an array of animal model species and, within species, a vast number of invaluable genotypes used in biomedical research. Embryo preservation uses a cryoprotectant in the freezing medium which allows sufficient dehydration to protect the blastomere during freezing. Following warming and dilution of the cryoprotectant, embryos are cultured to assess in vitro development. Transplantation of embryos into recipient females monitors in vivo development and thus biological competence. Cryobanked embryos are maintained until needed for rederivation. The primary focus of laboratory efforts is the study and optimization of cryobanking technology in mice, rabbits and rats. A major research finding is that embryo freezability is confounded and influenced markedly by genotype. Such responses have been examined in over 64 mouse genotypes, most of which display genotype- specific survival rates to standardized embryo freeze-warming procedures. Ancillary projects investigate the comparative aspects of improving long- term embryo storage with particular emphasis on cryoprotectants and enhancing methods for embryo freezing, warming, dilution and transfer. Efforts in the rabbit focus on collection procedures and preservation of embryos using a newly developed vitrification procedure. Initial attempts also have begun to recover rat embryos. Preliminary attempts also have been initiated to cryopreserve sperm. These techniques will be especially important for salvaging limited genetic material from individuals or genotypes with poor in vivo fertility.